Battery pack

ABSTRACT

Battery pack includes: a plurality of chargeable/dischargeable cylindrical cells; battery holder in which the plurality of cylindrical cells are disposed; and thermally conductive resin that closely adheres to cylindrical cells, which are stored in battery holder, in a thermally coupled state above battery holder. Battery holder includes: bottom plate including a plurality of holding grooves in which cylindrical cells are disposed; and partition walls that are disposed between holding grooves and between adjacent cylindrical cells. Partition walls are lower than the diameter of cylindrical cells disposed in holding grooves, thermally conductive resin is disposed between adjacent cylindrical cells above partition walls, and thermally conductive resin interconnects adjacent cylindrical cells.

This application is a U.S. national stage application of the PCTInternational Application No. PCT/JP2015/004668 filed on Sep. 14, 2015,which claims the benefit of foreign priority of Japanese patentapplication 2014-212551 filed on Oct. 17, 2014, the contents all ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a battery pack that includes aplurality of cylindrical cells and can certainly prevent a thermalrunaway of one cylindrical cell from causing a thermal runaway ofanother cylindrical cell near the one cylindrical cell.

BACKGROUND ART

A secondary cell can exhibit a thermal runaway due to various causessuch as an internal short-circuit and an overcharge. For example, when alithium-ion secondary cell exhibits a thermal runaway, the celltemperature can rapidly increase to 300° C. to 400° C. or more. When anysecondary cell exhibits a thermal runaway and causes a thermal runawayof its adjacent secondary cell, disadvantageously, many secondary cellsexhibit a thermal runaway and the energy of the thermal runawayextremely increases. This disadvantage can be eliminated by burying allor some of the cylindrical cells in a thermally conductive resin and byabsorbing, into the thermally conductive resin, the thermal energy ofthe cylindrical cell having exhibited the thermal runaway (PatentLiterature 1 and Patent Literature 2).

CITATION LIST Patent Literature

PTL 1: Unexamined Japanese Utility Model Publication No. H06-80260

PTL 2: Unexamined Japanese Patent Publication No. 2014-86342

SUMMARY OF THE INVENTION

In a battery pack of Patent Literature 1, as shown in FIG. 8, thermallyconductive resin 87 is filled into exterior case 83, and cylindricalcells 81 are buried in thermally conductive resin 87. In this batterypack, thermally conductive resin 87 can absorb the thermal energy ofburied cylindrical cells 81. However, disadvantageously, manufacturingthis battery pack takes much time and effort because thermallyconductive resin 87 is filled into whole exterior case 83 andcylindrical cells 81 are buried in thermally conductive resin 87. Thebattery pack is manufactured by disposing cylindrical cells 81 at fixedpositions in exterior case 83 and injecting thermally conductive resin87. However, disadvantageously, it is difficult to completely exhaustthe internal air and inject thermally conductive resin 87 withoutclearance in an injection process. When air remains in exterior case 83and an air pocket occurs, a thermally coupled state between cylindricalcells 81 and thermally conductive resin 87 degrades, and the thermalenergy of cylindrical cells 81 cannot be certainly and stablytransferred to thermally conductive resin 87.

A battery pack of Patent Literature 2 is manufactured in the followingprocesses, as shown in an exploded perspective view of FIG. 9:

battery core pack 90 is placed into bottom case 93 in the state wherethermally conductive resin 97 is filled into the bottom of bottom case93;

a lower part of each cylindrical cell 91 is dipped into fluidthermally-conductive resin 97; and

thermally conductive resin 97 is cured in this state.

This battery pack is manufactured by filling the thermally conductiveresin into the bottom case through a clearance in the battery core packin the state where the battery core pack is placed in the bottom case,and curing the thermally conductive resin. In this battery pack, bottomcase 93 is molded in a bottomed dish shape that prevents filledthermally conductive resin 97 from leaking to the outside. Regardingthis battery pack, in the state where battery core pack 90 is placed inbottom case 93 filled with fluid thermally-conductive resin 97, or inthe process of injecting fluid thermally-conductive resin 97 into bottomcase 93 having battery core pack 90, fluid thermally-conductive resin 97is apt to leak to the outside, and bottom case 93 must be left at restuntil fluid thermally-conductive resin 97 is cured. Therefore,disadvantageously, the workability is low and efficient mass productionis difficult.

The present invention has been developed for addressing thisdisadvantage. An important objective of the present invention is toprovide a battery pack that allows efficient mass production whileeffectively preventing the induction of a thermal runaway of acylindrical cell.

A battery pack of the present invention includes: a plurality ofchargeable/dischargeable cylindrical cells; a battery holder for storingthe plurality of cylindrical cells disposed on the same horizontalplane; and a thermally conductive resin that closely adheres to thecylindrical cells, which are stored in the battery holder, in athermally coupled state above the battery holder. The battery holderincludes: a bottom plate having a plurality of holding grooves in whichthe cylindrical cells are disposed; and partition walls disposed betweenholding grooves and between adjacent cylindrical cells. The partitionwalls are lower than the diameter of the cylindrical cells disposed inthe holding grooves. The thermally conductive resin is disposed betweenthe adjacent cylindrical cells above the partition walls, andinterconnects the adjacent cylindrical cells in a thermally coupledstate.

A battery pack of the present invention allows efficient mass productionwhile securing the safety by effectively preventing the induction of athermal runaway of a cylindrical cell. That is because the battery packof the present invention has the following structure: a thermallyconductive resin is applied to the valleys between the cylindrical cellsarranged in parallel in a battery holder having an upper opening; andthe applied thermally conductive resin interconnects the adjacentcylindrical cells in a thermally coupled state and prevents theinduction of a thermal runaway. Especially, in the battery pack of thepresent invention, the upper part of the battery holder is open, and thethermally conductive resin is applied, through the opening, to thevalleys between the adjacent cylindrical cells. Therefore, the thermallyconductive resin can be easily applied, and can be applied in the statewhere the thermally conductive resin certainly and closely adheres tothe surfaces of the cylindrical cells, namely in an idealthermally-coupled state. The thermally conductive resin applied in thisstate efficiently absorbs the thermal energy of a cylindrical cellhaving exhibited a thermal runaway, and radiates, via the thermallyconductive resin, the absorbed thermal energy to another cylindricalcell that is connected to the former cylindrical cell in the thermallycoupled state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical sectional view of a battery pack in accordance withone example of the present invention.

FIG. 2 is a sectional view taken along line II-II on the battery pack ofFIG. 1.

FIG. 3 is an exploded sectional view showing the manufacturing processof the battery pack of FIG. 1.

FIG. 4 is a vertical sectional view of a battery pack in accordance withanother example of the present invention.

FIG. 5 is a sectional view taken along line V-V on the battery pack ofFIG. 4.

FIG. 6 is an exploded perspective view showing the connection structurebetween lead plates and cylindrical cells stored in a battery holder.

FIG. 7 is a vertical sectional view of a battery pack in accordance withyet another example of the present invention.

FIG. 8 is a sectional view of a conventional battery pack.

FIG. 9 is an exploded perspective view of another conventional batterypack.

DESCRIPTION OF EMBODIMENT(S)

Hereinafter, examples of the present invention are described withreference to the accompanying drawings. The following examples showbattery packs for embodying the technical ideas of the presentinvention. The present invention is not limited to the following batterypacks. In this description, members shown in the scope of claims are notlimited to the members of the examples.

Each of battery packs 100 and 200 shown in FIG. 1 to FIG. 5 includes thefollowing components:

a plurality of chargeable/dischargeable cylindrical cells 1;

battery holder 2 for guiding the plurality cylindrical cells 1 andarranging them in parallel on the same horizontal plane;

thermally conductive resin 7 closely adhering, in a thermally coupledstate, to exposed surfaces 1A of cylindrical cells 1 stored in batteryholder 2; and

bottom case 3 in which battery holder 2 is disposed.

The battery pack of the present example has an above-mentionedstructure, and can further include holding grooves each having a shapefollowing the surface of each cylindrical cell.

In the battery pack of the present example, the height of each partitionwall from the bottom plate can be set at ¼ or more and ¾ or less of thediameter of each cylindrical cell.

In the battery pack of the present example, a peripheral wall having aheight equivalent to the diameter of each cylindrical cell can beerected around the bottom plate.

In the battery pack of the present example, a lead plate connected to anelectrode of each cylindrical cell is disposed in an electrode windowopened in the peripheral wall, and can block the electrode window.

The battery pack of the present example includes a bottom case having anupper opening in which a battery holder is disposed, and a circuit boardthat is disposed between the battery holder and the bottom case and hasa protective circuit of the cylindrical cells.

In the battery pack of the present example, the thermally conductiveresin can take a non-fluid paste form in an uncured state.

In the battery pack of the present example, the thermally conductiveresin can include any one of a silicon resin, an urethane resin, and anepoxy resin.

The battery pack of the present example includes a lid case that coversthe upper opening of the battery holder and is connected to the bottomcase. The lid case is made to closely adhere to the thermally conductiveresin in the thermally coupled state and can block the upper openings ofboth of the battery holder and the bottom case.

In the battery pack of the present example, the thermally conductiveresin includes a low-temperature molding resin made of a thermoplasticresin whose melting temperature is 120° C. or more and 250° C. or less.The battery holder in which the cylindrical cells are disposed at fixedpositions is insert-molded in the low-temperature molding resin and isfixed to a fixed position, the low-temperature molding resin is made toclosely adhere to cylindrical cells 1 in the thermally coupled state,and the thermally conductive resin serves as a lid case for blocking theupper opening of the bottom case.

In the battery pack of the present example, battery holders are stackedin a plurality of stages, and the thermally conductive resin filled intothe battery holders can be formed so that an upper battery holder andlower battery holder 2 closely adhere to each other in the thermallycoupled state.

Therefore, the battery pack of the present example can prevent theinduction of a thermal runaway by restricting the temperature increaseof the cylindrical cells that is caused by the thermal energy of acylindrical cell having exhibited a thermal runaway. Furthermore,partition walls are disposed between the cylindrical cells, so that thepartition walls also absorb the thermal energy of the cylindrical cellhaving exhibited a thermal runaway via the thermally conductive resinapplied to the valleys. The thermal energy absorbed by the partitionwalls is thermally transferred to the bottom plate of the battery holderand is radiated, so that rapid temperature increase of the partitionwalls is also suppressed. Therefore, in the battery pack, the thermallyconductive resin can be easily and certainly applied in an idealthermally-coupled state, and a combination of the applied thermallyconductive resin and the partition walls can certainly prevent theinduction of a thermal runaway of a cylindrical cell.

The battery pack of the present example allows an efficient andinexpensive mass production while securing the safety by effectivelypreventing the induction of a thermal runaway of a cylindrical cell.That is because the battery pack of the present invention includes thefollowing structure: a thermally conductive resin includes alow-temperature molding resin made of a thermoplastic resin; the batteryholder in which the cylindrical cells are disposed at fixed positions isinsert-molded in the low-temperature molding resin and is fixed to afixed position; the low-temperature molding resin is made to closelyadhere to the cylindrical cells in the thermally coupled state; and thethermally conductive resin is used also as a lid case for blocking theupper opening in the bottom case. In the battery pack of the presentexample, especially, the battery holder in which the cylindrical cellsare disposed at the fixed positions is insert-molded in the thermallyconductive resin of the low-temperature molding resin, so that thethermally conductive resin can be certainly made to closely adhere tothe surfaces of the cylindrical cells and can be disposed in the idealthermally-coupled state. The thermally conductive resin in this stateefficiently absorbs the thermal energy of a cylindrical cell havingexhibited a thermal runaway, and radiates, via the thermally conductiveresin, the absorbed thermal energy to another cylindrical cell that isconnected to the former cylindrical cell in the thermally coupled state.

In the battery pack of the present example, a thermally conductive resinincludes a low-temperature molding resin, and the low-temperaturemolding resin is used also as a lid case for blocking the upper openingin the bottom case. Therefore, it is not required to use a lid case madeof another member in order to block the upper opening in the bottomcase, and to connect the lid case to the bottom case. Therefore,extremely efficient and inexpensive mass production is allowed. The lidcase does not need to be used, so that the whole battery pack can bethinned. Furthermore, the surface of the thermally conductive resin isexposed to the outside, so that the heat is efficiently radiated fromthe surface of the thermally conductive resin, the temperature increaseof the thermally conductive resin can be reduced, and the induction of athermal runaway of a cylindrical cell can be more effectively prevented.

Cylindrical cell 1 is a lithium-ion secondary cell. As the cylindricalcell, a chargeable/dischargeable secondary cell such as a nickel-cadmiumcell or nickel-metal-hydride battery, especially a cell that generatesheat of a high temperature in the use state, can be used.

Battery holder 2 is entirely made of plastic as an insulating material,and is formed in a box shape having an upper opening by disposingperipheral wall 22 around bottom plate 21 perpendicularly to bottomplate 21. Bottom plate 21 includes a plurality of holding grooves 23 forguiding cylindrical cells 1 and holding them at fixed positions on thesame horizontal plane. Bottom plate 21 includes holding grooves 23 eachhaving a shape following the surface of each cylindrical cell 1, and ismolded in a wave shape. Bottom plate 21 closely adheres to the lowersurfaces of cylindrical cells 1, and cylindrical cells 1 are disposed ina thermally coupled state. Each holding groove 23 of bottom plate 21 hasa width of ½ or less and more than ¼ of the whole circumference of eachcylindrical cell 1, and is molded in the shape following the surface ofeach cylindrical cell 1. Wave-shaped bottom plate 21 includes, betweenholding grooves 23, partition walls 24 to be disposed between adjacentcylindrical cells 1. Partition walls 24 are lower than the diameter ofcylindrical cells 1 disposed in holding grooves 23, and, ideally, aremolded at a height of about a half of the diameter of cylindrical cells1, as shown in FIG. 1, FIG. 3, and FIG. 4. Although not shown, theheight of each partition wall 24 from bottom plate 21 can be set at ¼ ormore and ¾ or less of the diameter of cylindrical cells 1.

In battery holder 2, the height of peripheral wall 22 is setsubstantially the same as the diameter of cylindrical cells 1. In otherwords, the upper end of peripheral wall 22 and the upper ends ofcylindrical cells 1 are arranged on the same plane, and cylindricalcells 1 are disposed inside peripheral wall 22. In the battery holder,the peripheral wall can be made lower than the upper surfaces of thecylindrical cells. Especially, in an applied and uncured state,thermally conductive resin 7 taking a non-fluid paste form does not flowdown when it is applied to the valleys and the upper surfaces ofcylindrical cells 1. Therefore, even when peripheral wall 22 is madelow, applied thermally conductive resin 7 does not flow down to theoutside of battery holder 2.

The sectional views of FIG. 1 and FIG. 4 are sectional views obtained bycutting battery packs 100 and 200 orthogonally to the longitudinaldirection of cylindrical cells 1. Battery holder 2 shown in thesediagrams has a curved shape following the outer surfaces of cylindricalcells 1 in the range including bottom plate 21 and side walls 22A ofperipheral wall 22. Here, side walls 22A are disposed on the oppositesides of whole cylindrical cells 1. In battery holder 2, cylindricalcells 1 on the opposite sides can be placed in holding grooves 23 inbottom plate 21 and can be disposed so as to prevent a positionaldisplacement. That is because cylindrical cells 1 can be disposed atfixed positions via holding grooves 23 and side walls 22A on theopposite sides.

The sectional views of FIG. 2 and FIG. 5 are sectional views obtained bycutting battery packs 100 and 200 along the longitudinal direction ofcylindrical cells 1. These diagrams show the cross sections obtained bycutting the battery packs at the positions of the valleys betweenadjacent cylindrical cells 1. In battery holder 2 disposed in bottomcase 3, as shown in FIG. 6, each of end-surface walls 22B of peripheralwall 22 includes opening electrode windows 25 in which metal lead plates5 are disposed. Here, end-surface walls 22B are disposed on the oppositeends of cylindrical cells 1. Lead plate 5 is connected to the endelectrodes of adjacent cylindrical cells 1, and cylindrical cells 1 areinterconnected in series or in parallel. Lead plate 5 is fixed to theend electrodes of cylindrical cells 1 by spot welding. Electrode windows25 are disposed at positions facing the end electrodes disposed at theopposite ends of each cylindrical cell 1, and expose the end electrodesto the outside of end-surface walls 22B. Each electrode window 25 isblocked by lead plate 5 connected to the end electrode of cylindricalcell 1. In battery holder 2 in which electrode windows 25 are blocked bylead plates 5, even when thermally conductive resin 7 of a low viscosityis applied, thermally conductive resin 7 can be prevented from leakingto the outside of peripheral wall 22.

In battery holder 2 shown in FIG. 6, lead plates 5 are disposed onend-surface walls 22B in an engagement structure. Each end-surface wall22B includes, on the outside, positioning engagement portions 26 usedfor disposing lead plates 5 at fixed positions in the engagementstructure. Each positioning engagement portion 26 is smaller than theouter shape of each cylindrical cell 1, and opening electrode windows 25are disposed inside positioning engagement portion 26. Lead plates 5 arefitted into the inside of positioning engagement portions 26, and aredisposed at fixed positions of each end-surface wall 22B. The projectingelectrode and flat electrode that are disposed at the opposite ends ofeach cylindrical cell 1 are disposed inside end-surface walls 22B, andare disposed in the state where they are exposed to the outside throughelectrode windows 25. The projecting electrode and flat electrode thatare exposed through electrode windows 25 come into contact with leadplates 5 disposed in electrode windows 25, and are fixed by spotwelding. In battery holder 2 of the present invention, electrode windows25 can be certainly blocked by lead plates 5 disposed in positioningengagement portions 26.

Bottom case 3 has a box shape having an upper opening, and batteryholder 2 is disposed at a fixed position inside it. Battery holder 2 isdisposed at the fixed position in an engagement structure in bottom case3. The engagement structure between bottom case 3 and battery holder 2can include a structure in which one of battery holder 2 and bottom case3 has a fitting projection and the other has a fitting recess. In thisengagement structure, by guiding the fitting projection to the fittingrecess, battery holder 2 and bottom case 3 can be disposed at fixedpositions. The following structure may be employed: bottom case 3includes a positioning recess for guiding battery holder 2 to the fixedposition; battery holder 2 is guided to the positioning recess disposedin bottom case 3; and battery holder 2 is disposed at the fixed positionin bottom case 3.

In battery packs 100 and 200 in which battery holder 2 and bottom case 3are connected to the fixed positions in the engagement structure,battery holder 2 can be easily disposed at the fixed position in bottomcase 3. However, battery holder 2 does not necessarily need to bedisposed at the fixed position in bottom case 3 in the engagementstructure. The reasons are as follows. In battery pack 100 shown in FIG.1 and FIG. 2, thermally conductive resin 7 is made to adhere to lid case4, and battery holder 2 can be disposed at the fixed position. Inbattery pack 200 shown in FIG. 4 and FIG. 5, battery holder 2 can beinsert-molded in thermally conductive resin 7 of low-temperature moldingresin, and can be fixed to the fixed position.

Circuit board 6 is disposed between battery holder 2 and bottom case 3.Circuit board 6 includes electronic component 8 such as a protectivecircuit. For example, the protective circuit of circuit board 6includes: a detection circuit for detecting the voltage, remainingcapacity, and temperature of each cylindrical cell 1; and a switchingelement that is turned on or off in response to the cell data detectedby the detection circuit. When the voltage, remaining capacity, ortemperature of cylindrical cell 1 exceeds a set range, the protectivecircuit turns off the switching element to block the current andprotects cylindrical cell 1. Circuit board 6 is connected to cylindricalcells 1 via single-wire lead lines or lead plate 5, and disposed at afixed position of battery holder 2. Circuit board 6 can be disposed atthe fixed position also by the following processes: forming, in thelower surface of battery holder 2, a fitting recess into which circuitboard 6 is fitted or a positioning projection for positioning circuitboard 6; and engaging circuit board 6 with the fitting recess orpositioning projection.

Thermally conductive resin 7 is a silicon resin taking a paste form inan uncured state. Thermally conductive resin 7, however, may include anurethane resin or an epoxy resin that is a resin taking a paste form inan uncured state. The thermal conductivity of thermally conductive resin7 can be increased by mixing a thermally conductive material into it. Asthe thermally conductive material, metal powder, carbon powder, orcarbon fiber can be employed. Preferably, an insulating material isemployed as thermally conductive resin 7. When electrically-conductivemetal powder is employed as the mixed thermally conductive material, theelectric conductivity of thermally conductive resin 7 can be decreasedby reducing the additive amount. That is because an insulating resin isdisposed around the thermally conductive material and the thermallyconductive material is buried in a state insulated by the insulatingresin. The heat capacity of thermally conductive resin 7 per unit volumecan be increased by mixing, into it, powder of a high heat capacity—forexample, inorganic powder. Thermally conductive resin 7 having a highheat capacity can absorb much thermal energy from cylindrical cells 1,so that the induction of a thermal runaway can be more effectivelyprevented.

FIG. 3 is an exploded sectional view showing the manufacturing processof battery pack 100 of FIG. 1. In this process, thermally conductiveresin 7 is applied to cylindrical cells 1. As shown in FIG. 3, thermallyconductive resin 7 is applied to the valleys between cylindrical cells 1and interconnects adjacent cylindrical cells 1 in a thermally-coupledstate. Therefore, employed thermally conductive resin 7 has a viscosityallowing the following process: thermally conductive resin 7 remains inthe valleys between cylindrical cells 1 in the applied and uncuredstate, and can interconnect adjacent cylindrical cells 1 in athermally-coupled state. Thermally conductive resin 7 taking a non-fluidpaste form in the applied and uncured state does not flow down when itis applied to the valleys between cylindrical cells 1, remains and iscured in the valleys, and can interconnect adjacent cylindrical cells 1in an ideal thermally-coupled state. Thermally conductive resin 7 can bevery easily applied and is cured in the applied state, and hence cancertainly interconnect adjacent cylindrical cells 1 in thethermally-coupled state. Applied thermally conductive resin 7 does notflow or move before it is cured, so that the handling in a period fromthe application to the cure is simple and efficient mass production isallowed.

However, the battery pack of the present invention is not limited tothermally conductive resin 7 taking a non-fluid paste form in theuncured state. The reason is as follows. A battery pack includingbattery holder 2 in which applied thermally conductive resin 7 as anuncured resin is prevented from leaking from the inside of peripheralwall 22 can also employ thermally conductive resin 7 having a viscositythat allows flow down of the resin from the valleys to the gaps betweenbottom plate 21 and cylindrical cells 1. In this battery pack, thermallyconductive resin 7 applied to the valleys between cylindrical cells 1does not leak from the inside of battery holder 2 to the outside, sothat thermally conductive resin 7 is filled into the valleys betweencylindrical cells 1 through the gaps between bottom plate 21 andcylindrical cells 1.

In battery pack 100 of FIG. 3, thermally conductive resin 7 is appliedto not only the valleys between cylindrical cells 1 but also the tops ofcylindrical cells 1. In battery pack 100 of FIG. 3, thermally conductiveresin 7 is applied in two rows to the top of central cylindrical cell 1,and is applied in one row to the tops of other cylindrical cells 1. Inbattery pack 100, thermally conductive resin 7 is applied to the valleysand to the tops of cylindrical cells 1, and then thermally conductiveresin 7 connects lid case 4 to bottom case 3 in the uncured state.Thermally conductive resin 7 taking a paste form in the uncured state isflattened and made to closely adhere to the inner surface of lid case 4.In battery pack 100, thermally conductive resin 7 applied to the valleysinterconnects adjacent cylindrical cells 1 in the thermally coupledstate, and thermally conductive resin 7 applied to the tops connectscylindrical cells 1 to lid case 4 in the thermally coupled state.Therefore, the thermal energy of cylindrical cell 1 that generates heatis transferred to and absorbed by thermally conductive resin 7 and itsadjacent cylindrical cells 1, and also is absorbed by lid case 4 andradiated to the outside. In battery pack 100, therefore, the thermalenergy of cylindrical cell 1 having exhibited a thermal runaway isefficiently absorbed by thermally conductive resin 7 and othercylindrical cells 1, the heat is effectively radiated from lid case 4,and the induction of a thermal runaway can be more certainly prevented.

In battery pack 100 of FIG. 1 to FIG. 3, the end surfaces of theperipheral walls disposed in lid case 4 and bottom case 3 areultrasonically welded to each other, or are adhesively interconnected.One of the end surfaces of lid case 4 and bottom case 3 includes aridge, and the other includes a connection groove for guiding the ridge.Lid case 4 and bottom case 3 are connected to fixed positions byinserting the ridge into the connection groove. Although not shown, lidcase 4 and bottom case 3 may be interconnected by screwing a lockingscrew through one case into a boss disposed in the other case. The endsurfaces of the peripheral walls of lid case 4 and bottom case 3 areinterconnected, and the inside of these cases is blocked. Furthermore,output connecter 9 connected to circuit board 6 is fixed to bottom case3. Output connecter 9 has an output terminal and a signal terminal, ischarged or discharged via the output terminal, and communicates with aninstalled apparatus via the signal terminal. However, the battery packmay have the following structure: an output connecter is not disposed;connection terminals formed of the output terminal and signal terminalare fixed to the circuit board; and these connection terminals arepulled out of the bottom case and connected to the outside.

In battery pack 200 of FIG. 4 and FIG. 5, thermally conductive resin 7includes a low-temperature molding resin made of a thermoplastic resinwhose melting temperature is 120° C. or more and 250° C. or less.Battery pack 200 is molded by the following processes: disposingcylindrical cells 1 at fixed positions of battery holder 2; temporarilyfixing core pack 10 that is produced by integrally interconnectingcircuit board 6, bottom case 3, and battery holder 2 to a fixed positionof a die for molding the low-temperature molding resin; heating amolding chamber of the die; and injecting molten thermally conductiveresin 7. After thermally conductive resin 7 is cooled, thermallyconductive resin 7 is taken out of the die, and thus battery pack 200 inwhich core pack 10 of the battery is insert-molded in thermallyconductive resin 7 is produced. Battery pack 200 is produced byinsert-molding core pack 10 of the battery in thermally conductive resin7 of the low-temperature molding resin. Thermally conductive resin 7closely adheres to the surfaces of cylindrical cells 1 that are exposedto the upper opening of battery holder 2, and interconnects allcylindrical cells 1 in the thermally coupled state.

In battery pack 200 of FIG. 4 and FIG. 5, molded thermally conductiveresin 7 is used also as lid case 14. Therefore, battery pack 200 doesnot require a lid case as another member, and does not require a processof connecting another molded lid case to bottom case 3. Therefore, thecomponent cost can be reduced, the manufacturing process can besimplified, and the manufacturing cost can be reduced. Since thermallyconductive resin 7 is exposed to the outside and the heat is radiated,the heat radiation characteristic of thermally conductive resin 7 can beimproved. Furthermore, the heat radiation characteristic can beimproved, by disposing radiation fins 15 on thermally conductive resin 7as shown by dashed lines in the drawings.

Cylindrical cells 1 that are insert-molded in the low-temperaturemolding resin as thermally conductive resin 7 closely adhere tothermally conductive resin 7, and adjacent cylindrical cells 1 areinterconnected in the thermally coupled state. The thermoplastic resinof the low-temperature molding resin is a polyamide resin. Another resinsuch as an epoxy resin can be added to the polyamide resin. A polyamideresin containing an added epoxy resin has an adhesive force tocylindrical cells 1 higher than that of only a polyamide resin.

A polyamide resin has a low softening temperature, and also has a lowviscosity during melting, so that it can be molded at a lowertemperature and a lower pressure compared with another thermoplasticsynthetic resin. In addition, a polyamide resin can be taken out of themolding chamber of the die. The low-temperature molding resin molded ata low temperature and a low pressure can shorten the time taken formolding, and can reduce the adverse effect of the heat and injectionpressure during the resin molding on an electronic component or thelike. In the present invention, however, the low-temperature moldingresin is not limited to the polyamide resin. A resin other than thepolyamide resin—for example, polyurethane resin—can be employed.Furthermore, as the low-temperature molding resin, a thermoplastic resinsuch as a polyethylene resin, acrylic resin, and polypropylene resin canbe employed, as long as the thermoplastic resin can improve the heatresistance of cylindrical cells 1 and electronic component 8 that areinsert-molded.

In the present exemplary embodiment, a plurality of cylindrical cells 1are disposed on the same plane using one battery holder 2. As batterypack 300 of FIG. 7, however, another battery holder 2 including aplurality of cylindrical cells 1 disposed on the same plane may bestacked on one battery holder 2 in two stages. Battery holders 2 may bestacked in three or more stages. In other words, battery holders 2 maybe stacked in a plurality of stages. At this time, thermally conductiveresin 7 filled into lower battery holder 2 can make upper battery holder2 closely adhere to lower battery holder 2 in the thermally coupledstate. Thus, the battery capacity can be increased solely by increasingthe volume corresponding to the thickness of battery holder 2. Asbattery pack 200 of FIG. 4, molded thermally conductive resin 7 may beused also as lid case 14.

In the present exemplary embodiment, partition walls 24 are used ascurved coupling portions by forming bottom plate 21 in a curved shapefollowing the outer surfaces of cylindrical cells 1. However, the bottomplate may be made flat, and partition walls may be vertically erectedfrom the flat plate.

A battery pack of the present invention includes a plurality ofcylindrical cells, and can be safely used by preventing the induction ofa thermal runaway of a cylindrical cell.

The invention claimed is:
 1. A battery pack comprising: a plurality ofchargeable/dischargeable cylindrical cells; a battery holder for storingthe plurality of cylindrical cells disposed on the same horizontalplane; and a thermally conductive resin closely adhering to theplurality of cylindrical cells in a thermally coupled state above thebattery holder, the plurality of cylindrical cells being stored in thebattery holder, wherein the battery holder includes: a bottom platehaving a plurality of holding grooves in which the plurality ofcylindrical cells are disposed; and partition walls disposed between theplurality of holding grooves and between adjacent cylindrical cells, ofthe plurality of cylindrical cells, wherein a height of each of thepartition walls is lower than a diameter of each of the plurality ofcylindrical cells disposed in the plurality of holding grooves, andwherein the thermally conductive resin is disposed between the adjacentcylindrical cells above the partition walls, and interconnects theadjacent cylindrical cells, wherein each of the plurality of holdinggrooves is formed in a shape following a surface of each of theplurality of cylindrical cells, wherein the thermally conductive resinmakes an upper battery holder, a lower battery holder, and the partitionwalls of the lower battery holder, wherein each of the battery holdersclosely adhere to each other in a thermally coupled state and arestacked in a plurality of stages, wherein each of the battery holdersstore the plurality of cylindrical cells, wherein the thermallyconductive resin is disposed between the adjacent cylindrical cellsabove the partition walls, and interconnects the adjacent cylindricalcells, and wherein the thermally conductive resin is disposed betweenthe upper battery holder and the lower battery holder.
 2. The batterypack according to claim 1, wherein the height of each of the partitionwalls from the bottom plate is ¼ or more and ¾ or less of the diameterof each of the plurality of cylindrical cells.
 3. The battery packaccording to claim 1, wherein a peripheral wall having a heightequivalent to the diameter of each of the plurality of cylindrical cellsis erected around the bottom plate.
 4. The battery pack according toclaim 3, wherein a lead plate coupled to an electrode of each of theplurality of cylindrical cells is disposed in an electrode window openedin the peripheral wall, and blocks the electrode window.
 5. The batterypack according to claim 1, further comprising: a bottom case having anupper opening, the battery holder being disposed in the bottom case; anda circuit board disposed between the battery holder and the bottom case,and having a protective circuit of the plurality of cylindrical cells.6. The battery pack according to claim 1, wherein the thermallyconductive resin takes a non-fluid paste form in an uncured state. 7.The battery pack according to claim 1, wherein the thermally conductiveresin includes any one of a silicon resin, an urethane resin, and anepoxy resin.
 8. The battery pack according to claim 5, furthercomprising a lid case covering an upper opening of the battery holderand coupled to the bottom case, wherein the lid case is made to closelyadhere to the thermally conductive resin in a thermally coupled state,and blocks the upper opening of the bottom case.
 9. The battery packaccording to claim 5, wherein: the thermally conductive resin includes alow-temperature molding resin made of a thermoplastic resin whosemelting temperature is 120° C. or more and 250° C. or less, the batteryholder storing the plurality of cylindrical cells disposed at fixedpositions is insert-molded in the low-temperature molding resin and isfixed to a fixed position, the low-temperature molding resin is made toclosely adhere to the plurality of cylindrical cells in a thermallycoupled state, and the thermally conductive resin serves as a lid casefor blocking the upper opening of the bottom case.